In order to improve both performance and integrity of integrated circuit chips, feature sizes of devices are scaled down continually in view of Moore's law, which nowadays have already reached into the nanometer regime. Traditional planar bulky Si CMOS technology cannot any more boost improvement in device performance and decrease power consumption at the meantime of improving integrity of circuits. Consequently, device parameters fluctuate randomly and the threshold voltage cannot be scaled down proportionally, which further brings limits on enhancement of whole device performance. In technology node of 45 nm and below, dramatically soaring short-channel effects also raise difficulties of further scaling down devices proportionally.
Fully depleted SOI (FDSOI) devices, which exhibit outstanding suppression of short-channel effects, excellent sub-threshold properties, small leakage currents and slight influence of random doping fluctuations, are regarded as preferred structures for replacing traditional bulky Si devices at technology node of 32 nm and below. FDSOI devices are usually configured with an ultra-thin (≦50 nm) SOI structure, thus decrease in thickness (≦50 nm) of buried oxide layer (BOX) can further improve device performance, lessen influences arising from self-heating effects, peripheral fields and the like. Besides, owing to introduction of a ground layer into the back face of ultra-thin BOX layer so as to enhance controls and regulations of back gates, such Ultra-Thin Body and BOX (UTBB) SOI devices are able to reduce electric fields coupling at source/drain regions and to increase controls of threshold voltages, such that they exhibit broad prospects of being utilized in applications of low power consumption. However, circuit area has been increased inevitably due to introduction of back gate contact and relevant wiring, thereby increasing manufacturing cost. Therefore, for UTBB SOI devices, how to find a balance between optimal device performance and costs has now become a critical problem that is waiting for a solution.